In the manufacture of paper, paper sheets containing water are carried by a felt from a wire part to a press part, in which water is expressed, and then the resulting paper sheets are fed to a drying part to finish them as final paper sheets. Thus, the felt acts as means for receiving wet paper sheets dewatered in the wire part to convey it to the press part, further squeezing the water out by passing it between two press rolls and smoothing surfaces of the wet paper sheets at the same time, and sending them to the drying part. Accordingly, the felt must have at least three functions, namely the function of serving as a conveyer for conveying the wet paper sheets, the function of squeezing the most possible water out of the wet paper sheets, and the function of smoothing the surfaces of the wet paper sheets. For this reason, the felt is required to be seamless, to be a fibrous structure excellent in water squeezability, elasticity and recovery, and to have a surface which does not produce unevenness on the finished paper sheets.
Recently, the papermaking speeds of paper machines become higher, and therefore the felts must also run resisting the high speed operations. For this reason, the felts also call for durability, and properties required for the felts have become higher and more precise. The papermaking felts have been shifted from the former type of woven wool felts to needled synthetic fiber felts, and polyamide fibers are used for fibrous batt layers or base fabrics.
Fibers exhibiting rubber-like elasticity, such as polyurethane elastic fibers, have formerly known. However, the elastic fibers are generally difficult to use as felt materials. It is difficult to card the elastic fibers with carding machines, and sufficient compactness can not be obtained on the needling thereof. When the elastic fibers are needle punched, only local portions mechanically stressed are largely deformed, and the original fiber arrangement is regained on the removal of the applied stress. As a result, the sufficient three-dimensional entanglement of the fibers can not be produced. The enforcement of the entanglement causes breakage and damage to the fibers, and uneven tension induced on the felt formation disturbs the formation of uniform felts. It has been therefore considered difficult to manufacture an uniform felt composed of the elastic fibers which are uniformly arranged and having stable qualities and properties like the felts composed of the conventional usual fibers.
It is therefore an object of the present invention to provide a needled felt for papermaking use excellent in elasticity, recovery, durability etc, overcoming the difficulty in manufacture of felt, especially in needling process, and maintaining properties of felt.
Other objects and novel features of the invention will be apparent from the following description and claims, taken in connection with the accompanying drawings.